Farm-scale Mapping of Soil Phosphorus and Potassium Fractions Using Geostatistical Technique

Phosphorus (P) and potassium (K) are two major nutrients for agricultural productivity and sustainability. The spatial variability maps of soil phosphorus and potassium content in surfacesoils collected through grid sampling technique were developed using geo-spatial technology for Indian Council of Agricultural Research-Indian Agricultural Research Institute (ICAR-IARI) farm, New Delhi, India. Soil available P content (NaHCO3-P) and P-fractions such as NaOH extractable-P(NaOH-P), citrate-bicarbonate extractable P (CB-P), citrate-bicarbonate-dithionite extractable-P(CBD-P) and HCl extractable-P (HCl-P) through sequential fractionation techniques and K fractions(available-K and non-exchangeable-K) were estimated. In geostatistical technique, exploratory data analysis and semivariogram analysis for P & K fractions were conducted and ordinary kriging was used for spatial interpolation and mapping. On average basis, among the P-fractions, Ca-boundphosphorus (HCl-P) had highest value followed by non-occluded Fe- and Al-bound-P (i.e. NaOH-P)and occluded-P within iron oxide and hydrous oxide (i.e. CBD-P). Soil available K in the farmranged from 43.9 to 839.3 mg kg-1 and non-exchangeable-K content was found to be in high to veryhigh level (820-1921 mg kg-1). Among the P & K fractions, occluded-P and Ca-bound P showed first order polynomial surface trend, which were removed before ordinary kriging interpolation. Semivariogram analysis of soil P- & K-fractions at the IARI farm indicated the effective spatial range dependency. Prediction maps of P- & K- fractions in the semiarid agricultural farm thorough ordinary kriging were found superior to log-normal ordinary kriging. The spatial variability map based fertilizer recommendation and management practices for major cropping systems in the farmarecrucial for precision nutrient management and sustainable agriculture.